Selecting Wood for Rot and Insect Resistance

Woodworkers notice that old-growth lumber seems to be more durable than juvenile wood, across different species. December 24, 2012

I have a project to replace balustrade railing on the exterior of a home. Would sapele be a good choice, or meranti? Existing railing and balusters are cedar, which rotted after 5 years. I asked the lumber yards and got two different answers about sapele/meranti. One yard said sapele is not for exterior. Other says it is.

Forum Responses
(Architectural Woodworking Forum)
Western red cedar: rated as durable to very durable in regard to decay resistance, though it is not resistant to insect attack.

Sapele: moderately durable to very durable in regard to decay resistance. Sapele is susceptible to insect attack.

Meranti (light red): non-durable in regard to decay resistance, and is also susceptible to insect attack.

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From contributor D:
I'll stick my neck out a bit and say it is no longer species that is the number one indicator of long service in exterior situations. I believe it is old growth. I say this after detailed observation over a long period and working with many exterior situations. The new WR cedar and redwoods are the opposite of dense, and the ring spacing is… generous. They will rot in short order. The old growth cedar and redwood is still performing well after as long as 100 years. I have seen poplar that is over 100 years old - with incredibly dense ring spacing - and it looks great. I have also seen new poplar sprout mushrooms after 3 years outside.

Therefore, the imports - sapele, African mahogany, Honduras mahogany, utile, Spanish cedar, and others are likely to be old growth and more resistant to rot. Old growth being the operative due to dense ring structure.

This is entirely unscientific, so I would love to see if there is any research in this area or other observers that would agree with what I am seeing.

From the original questioner:
I do agree on the old growth theory. Thanks for taking the time to reply. Customer told me the previous work was not 5 years old - he installed it 12 years ago. Still, 12 years is not much since he painted it every two years. We went with the cl cedar with stainless steel screws.

From contributor J:
I agree totally. There are pine windows here over 100 years old and still functioning. All tight growth ring material. Even a lot of the imported species you mentioned sometimes are marginal.

From contributor A:
My circa 1825 carriage house in CT had quartersawn eastern white pine clapboards that were completely neglected to the point of not having any paint! No rot in 185 years!

"Hard" red Meranti is definitely rot resistant. The soft light stuff is not. People on WOODWEB have reported about rotting cedar and redwood. Why waste sapele outside? It's a lovely wood. Hey, wait - what about those thousands of board feet of Hondu we used to make window sash and exterior doors?

From contributor N:
Another consideration is properly dried sapele. A lot of it out there is supposedly being re-kilned stateside. This stuff we have found to be substandard, with case hardening, checks, and fuzzing. I pretty much tire of hearing mills guarantee your money back. Time and money is wasted bundling it up and trucking it back. Trying to maintain a decent supply over the years gets hit and miss. Eventually, you'll get into lumber from different sources because the mills are always scouting around too. They all grade different too. I've seen normal q-sawn look sweeter than pattern grade. I built my boss a couple of doors ten years ago that he never put a finish on. They've been out in the weather all this time without a crack, and still flat. But that seemed like a different era. Seemed like all the mahogany, even only ten years ago, was nice. None of this probably has anything to do with rot, but if it's unworkable, it's no good to me.

From contributor O:
That is very interesting regarding the old growth. I can't disagree. There is a guy here in N Idaho who just sided his house in sapele. Dumb and waste of money in my opinion, but man, does it glisten in the sun!